The objective of the proposed project is to elucidate the mechanism(s) by which glucocorticoids exert their permissive action on glucagon and catecholamine control of hepatic carbohydrate metabolism. Preliminary studies with rat hepatocytes isolated from normal and adrenalectomized rats have confirmed earlier findings in perfused rat livers. The majority of the proposed studies will therefore be carried out with isolated hepatocytes and key findings will be verified using the perfused liver. A systematic study is proposed to examine the role of changes in the cAMP-dependent and cAMP-independent activation of glycogenolysis in the permissive action of glucocorticoids. It is planned to test the actions of glucagon, epinephrine, isoproterenol, phenylephrine, angiotensin and vasopressin on glycogenolysis, intracellular cAMP levels, and activities of enzymes involved in the cascade mechanism of glycogen phosphorylase activation. The role of Ca ions will also be examined by observing hormonal action in Ca ions -free media as well the changes in 45Ca-uptake and exchange induced by hormones. The site of permissive action on glucagon and catecholamine stimulation of hepatic gluconeogenesis will be examined by using various gluconeogenic substrates, tissue metabolite analyses, and assays of key enzyme activities, particularly that of pyruvate kinase.